I can tell what you think about how translation works by the way you write. If you think that's rude and condescending, I honestly don't care.
Anyway, "hiragana" is not a loanword in English at all. When used, it's treated as a proper noun for something that's only in a foreign language. So nothing you wrote about loanwords applies.
Hiragana, katakana and kanji are untranslated terms that are included in major English dictionaries. They are loan words. It is common for less-frequently used foreign words to not be inflected as plural if there is not a specific plural form from the parent language. This may be confusing in some contexts and a translation that includes a plural noun to help provide that context can be useful. However, in a poetic or literary use, sometimes intentionally not inflecting a plural is a choice.
Being rude and condescending is an inappropriate tone for this site which should be centered around discussion and curiosity. Further, you’ve made zero substantial argument for your position, contradicted yourself and failed to make a case.
Anyway, "hiragana" is not a loanword in English at all. When used, it's treated as a proper noun for something that's only in a foreign language. So nothing you wrote about loanwords applies.